The goal of this integrated biochemical, physiological and clinical program is to study mechanisms initiating and regulating the tissue factor-dependent pathway of blood coagulation during hemostasis and in pathologic states. Biochmical reactions will be studied in purified and plasma systems, utilizing activation peptide release assays to measure activation of factors IX and X and the ratio of factor VII clotting to amidolytic activity coupled with radioactivity profiles of labeled factor VII measure activation of factor VII. A major effort will be made to purify a previously undescribed plasma material that, with factor Xa, inhibits factor VIIa-tissue factor enzymatic activity and to delineate the mechanism of the inhibition. A second biochemical project will focus upon activation of factor VII. The extent of activation will be related to rates of tissue factor-dependent activation of factor IX and X to determine whether generation of minimal amounts of factor VIIa can yield maximum rates of activation of factors IX and X. The ability will be evaluated of phospholipid on activated platelets and of phospholipid on unperturbed human endothelial cells to support factor Xa and factor IXa-induced activation of factor VII. A third biochemical project will focus upon the ability of zymogen factor VII to interact with tissue factor formed on cultured human endothelial cells with resultant activation of factors IX and X. Antithrombin III and the above described plasma inhibitory material will be included in some reaction mixtures. In additional experiments, increasing amounts of preformed factor VIIa will be added to the incubation mixtures with factor VII. Physiologic experiments will be carried out in rabbits to determine if infusion of tissue factor or injection of endotoxin can deplete plasma of the inhibitory material required for neutralization of factor VIIa-tissue factor. Plasma inhibitory factor levels will also be measured in patients. A quantitative assay for plasma inhibitory factor has been designed for these purposes. Other clinical projects will include studies of (1) the importance of platelet factor V for hemostasis in patients with factor V anticoagulants, (2) the relation between antiprothrombin antibodies and the lupus anticoagulant, and (3) diagnostic techniques and manifestations of thrombosis in hereditary protein C and protein S deficiency.